Question

Assertion: The mesophyll of Pinus shows no distinction as mesophyll and palisade.
Reason: Parenchymatous cells are present in the mesophyll of Pinus.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
(c) If the assertion is true but the reason is false.
(d) If both the assertion and reason are false.

Answer 1

Hint: Mesophyll is the ground tissue that fills the structure of the leaf from the upper epidermis to the lower epidermis. In some plants like dicots, the mesophyll is divided into two-layer known as the palisade parenchyma and spongy parenchyma.

Complete Answer:
The mesophyll of Pinus which is a gymnosperm is not divided into palisade and spongy parenchyma. But there is the presence of parenchymatous cells in the mesophyll of Pinus. These parenchymatous cells consist of a thin wall and chloroplast in them and thus are responsible for conducting photosynthesis.

Additional information: Let us look at the type of mesophyll layers in detail.
Palisade parenchyma:
- Palisade parenchyma is made up of tall and long cells that are arranged vertical and parallel to each other.
- It is the main site of photosynthesis as there are more chloroplasts in them.
Spongy parenchyma:
- Spongy parenchyma is made up of round or oval cells that are loosely arranged below the palisade parenchyma.
- Due to the large intercellular spaces in them, their main function is to allow gaseous exchange.
- Photosynthesis occurs only during high sunlight intensity.
So, the correct option is ‘If both the assertion and reason are true but the reason is not a correct explanation of the assertion’.

Note:
- Mesophyll is not differentiated as spongy and palisade parenchyma in monocotyledonous leaves as well.
- Dicot leaf is known as the dorsiventral leaf as the upper surface has more stomata as compared to the lower surface.
- Whereas a monocot leaf is known as an isobilateral leaf due to the presence of stomata on both the upper and lower surfaces.